The objectives of the proposal deal with the determination of effects of silica dust inhalation on the immunological defence mechanisms which are involved in the pulmonary resistance to infection. To accomplish these aims groups of mice will be exposed to air-borne silica dioxide. These exposures will be followed by in vivo and in vitro assessments of humoral and cellular immune responses to a variety of antigenic stimulations. Other groups of mice will be infected intranasally with mouse-adapted influenza virus following their exposure to silica. An attempt will be made to relate any changes seen in the immune mechanisms to changes noticed in resistance to pulmonary infection with influenza virus.